Camouflage is the act of concealing something by modifying its appearance, so that an otherwise visible person or object is either rendered indiscernible from the surrounding environment or simulates an object or entity that is non-threatening to the viewer.
The present state of the art of camouflage is sufficiently effective to have generated a large industry focused on providing camouflage fabrics and clothing in diverse patterns. However, all of these camouflage materials have neglected an important part of the electromagnetic (EM) spectrum. At wavelengths just below the visible range of humans lies the ultraviolet spectrum. Scientists have recently discovered that almost all diurnal bird families, many fish species, some rodents, and some larger mammals, including deer, possess vision in the near-ultraviolet range of the electromagnetic spectrum. The near-ultraviolet spectrum—from 320-400 nm (UVA, henceforth “UV”)—complements the human visible spectrum from 400-750 nm.
This extended visual spectrum has not hitherto been taken into consideration by the makers and users of artificial camouflage fabrics. All objects in the natural world reflect some percentage of the ambient ultraviolet light, which can be perceived by an ultraviolet-sensitive viewer. A hunter, for example, will only be concealed from nearby animals if the light reflectivity of the hunter's clothing is similar to the reflectivity of the surrounding background at all wavelengths which are visible to the animals. Similarly, a soldier will only be hidden from antagonists who possess UV vision equipment if the UV reflectivity of the soldier's clothing matches his or her surroundings.
The need for UV camouflage is demonstrated in the animal kingdom. For example, the Arctic fox is white in winter, the same visible color as the ever-present snow. However, the fox's fur also reflects ultraviolet light at approximately eighty-five percent—the same degree of reflection as fresh snow. This is necessary because many of the prey species of the Arctic foxes have vision in the ultraviolet spectrum. Similarly, any attempt at camouflage by humans must provide the proper level of ultraviolet reflection in order to be fully successful in avoiding detection by UV-sensitive animals or by antagonists who possess UV vision equipment.
It can be difficult and/or impractical to provide clothing and/or other fabrics to hunters or soldiers which match both the visible and UV reflectances of various background environments, because environments having similar reflectances in the visible spectrum often have quite different reflectances in the near ultra-violet, and vice-versa. For example, FIG. 1A illustrates a soldier 100 as seen in visible light wearing camouflage clothing 102 which is effective in blending with the surrounding environment 104. In FIG. 1B, the same soldier 100 is shown in ultraviolet light, where the same clothing 102 stands out clearly in contrast with the surrounding vegetation 104, since the clothing reflects more than 50% of the UV light, while the surrounding vegetation reflects less than 10% of the UV. Some examples are presented in Table 1 below of the UV reflectivity of various environmental surfaces.
TABLE 1DIFFUSE REFLECTION OF NEAR-ULTRAVIOLET FROM SURFACES *SurfacePercent Diffuse ReflectionFresh snow85“Dirty” old snow50Dry dune sand22Dry white dune sand39Atlantic beach sand-wet9Sea foam (surf)39Green mountain grassland2Dry, parched grassland4.8Sandy turf3.3Deciduous trees (leaves)7Unpainted wood8.3White cement22Concrete pavement15.6Black asphalt11.7Granite boulder70Rough dark tree bark (oak)15Smooth medium tree bark (aspen)50White birch bark70Water5* Compiled from published studies and inventor's research, then averaged.
As a result of these differences in UV reflectivity, a camouflage fabric designed to match one specific environment in both the visible and UV would be unlikely to work well in other environments, even if they looked very similar in the visible range, i.e. to the human eye. Since it is typically impractical for soldiers and hunters to carry many different types of camouflage clothing and coverings, makers of camouflage fabrics have tended to ignore reflectivity in the near ultra-violet, and have focused instead on producing fabrics which work well at visible wavelengths for a wide variety of surrounding environments.
In particular, the military need for camouflage in the UVA spectrum (320-400 nm) has been almost entirely neglected. While some militaries have acknowledged the need to provide supplemental UV camouflage, this has been done only for snow conditions. The most recent U.S. Army Field Manual—FM 20-3 3-5:d—states in Chapter 2 under “Threat”:
“The enemy employs a variety of sensors to detect and identify US soldiers, equipment, and supporting installations. These sensors may be visual, near infrared (NIR), IR, ultraviolet (UV), acoustic, or multispectral/hyperspectral. They may be employed by dismounted soldiers or ground-, air-, or space-mounted platforms. Such platforms are often capable of supporting multiple sensors. Friendly troops rarely know the specific sensor systems or combination of systems that an enemy employs . . . .”
And in section 2-16 under “ULTRAVIOLET” the manual states:
“The UV area is the part of the EM spectrum immediately below visible light. UV sensors are more important in snow-covered areas, because snow reflects UV energy well and most white paints and man-made objects do not reflect UV energy very well. Photographic intelligence systems with simple UV filters highlight military targets as dark areas against snow-covered backgrounds. These backgrounds require specially designed camouflage that provides a high UV reflectance . . . .
In Chapter 3, Section I 3-5 d the same manual states under “UV Sensors”:
“UV sensors are a significant threat in snow-covered areas. Winter camouflage paint patterns, the arctic LCSS, and terrain masking are the critical means for defending against these sensors; any kind of smoke will defeat UV sensors. Field-expedient measures, such as the construction of snow walls, also provide a means of defeating UV sensors.”
Digital technology has created vast improvements in real-time acquisition of UV images. A belligerent can purchase a used camcorder for one hundred dollars over the Internet, and then quickly convert the device to provide clear, real-time imaging in the near-UV/Vis/near-IR; that is, the wavelengths from 330 nm through 1250 nm. By using a lens filter that passes only UV, an enemy can clearly discern fine detail that would not otherwise be visible, including soldiers wearing the most advanced personal camouflage, such as the U.S. Army UCP (Universal Camouflage Pattern) Delta or the recent U.S. Army OCP (Operation Enduring Freedom Camouflage Pattern, a.k.a., MultiCam® by Crye Precision, Inc.). Both of these camouflage patterns stand out boldly in the UV against a background of foliage, as the albedo (percentage of diffuse reflectance) in the UV of green plants averages 3-7% (very dark), while the camouflage reflects, overall, in the range of 20-70% (quite bright). Other environments are just as unforgiving in the ultraviolet. Sandy turf, depending upon the silicates involved, may reflect as little as 3.3% in the UV, while many of the tans and grays used in military and civilian camouflage reflect more than 50% in the UV.
What is needed, therefore, is a system for providing camouflage clothing, coverings, and other fabrics which can match the reflectivity of a variety of background environments at both visible and near ultraviolet wavelengths, without requiring a hunter or soldier to carry burdensome equipment and/or redundant fabrics.